This project deals with the biosynthesis, localization, and regulaton of avian RNA tumor virus proteins in infected and uninfected cells. Viral related proteins are isolated by immune precipitation, using specific antisera prepared against virion proteins, and fractionated by polyacrylamide gel electrophoresis. Further characterization includes double-label tryptic peptide mapping and relative ordering of the peptides. These methods are being applied to a study of the organization and metabolism of polyproteins related to reverse transcriptase biosynthesis as well as to functional mapping of the products of the src gene by using cells infected with non-defective and mutant avian leukemia and sarcoma viruses. Other research involves a detailed analysis of an array of endogeous oncornavirus-specific proteins in tissues of normal uninfected chicken embryos. We propose to study the apparent tissue-specificity of these proteins as well as their organization, interaction with exogenous viruses, and possible role in differentiation and transformation. Additional proposed stuies will involve the polyproteins synthesized by the defective acute leukemia viruses and the nature of spontaneously relased recombinant viruses. A major objective here is to investigate the idea that new viral information can be generated by recombination between exogenous viruses and endogenous viral information.